1. Field of the Invention
The present invention relates to "descenders" for use in a abseils and in particular to an improved descender of the type which incorporates a self acting brake.
2. Technical Considerations and Prior Art
Abseils is a technique used to descend steep surfaces, such as cliff faces, and is often used by persons involved in activities such as mountain climbing, canyoning and caving. In order to abseil down a cliff face, one end of a rope is made fast at the top of the cliff and the person making the descent then slides down the rope. The rope is passed either around the body of the person or more usually through a descender attached to a harness worn by the person, such that the passage of the rope around the body or through the descender provides sufficient friction to slow the rate of descent to a safe speed. A descender comprises rope engaging surfaces over which the rope travels to provide frictional engagement between the rope and the descender. The rate of descent is normally controlled by holding the free end of the rope to control the tension on the rope where it enters the descender, and thereby to control the degree of frictional engagement between the rope and the descender which in turn controls the rate of descent.
Descenders used in an abseil vary greatly in performance and complexity, there being a variety of relatively simple devices which rely on frictional engagement between the rope and metal rings or racks about which the rope is wrapped and a number of more complex descenders which incorporate a braking mechanism, thereby enabling the friction between the rope and the descender to be varied. The earliest of these more complex devices had a handle or lever which when operated tended to increase the friction between the descender and the rope, however, this type of descender was not a great improvement over the more simple devices, as the brake was not self engaging, and therefore if the user was knocked unconscious he would fall in the same way as the user of the earlier devices.
The present invention belongs to a class of descenders wherein the variable braking action of the descender increases when the handle is released. Usually the force required to initiate the braking action is provided by the frictional engagement of the descender with the rope travelling therethrough, however, it is also possible to have arrangements which are operated by springs. Spring operated arrangements have the disadvantage that the restoring force of the spring may reduce with age or the spring may become damaged without this being noticed by the user, thereby decreasing the effectiveness of the descender.
All of the prior art descenders incorporating non-sprung self-engaging braking suffer from the problem that the maximum friction achieved by the descender when the brake actuates itself is not always sufficient to completely stop a person who is falling, such as when the person has been knocked unconscious. Examples of such prior art descenders may be studied in French Patent Publication Nos. 2,394,303, 2,430,388, 2,451,752 and 2,478,475 in the names Paul and Pierre Petzl, and West German Patent Publication No. 2,439,678 in the name Wolfgang Siersch. Examples of other lowering devices and rope brakes are described in U.S. Pat. No. 1,370,306 in the name H. J. Griest, U.S. Pat. No. 933,685 in the name J. H. Wray, British Pat. No. 1,125,774 in the name Marcel Jules Odilon Lobelle and British Pat. No. 1,568,614 in the name CATU SA, however, none of these prior art devices provide the simplicity of construction or operation which is achieved with the descender of the present invention.